1. Field of the Invention
The present invention relates to imaging systems. More specifically, the present invention relates to circuits and systems for processing the outputs of pyroelectric detectors used in night vision systems.
2. Description of the Related Art
Night vision systems are well known in the art. Night vision systems typically include a cryogenically cooled linear detector array with an associated cryogenic subsystem, a scanning system which moves a two dimensional image across the array, and a refractive optical system which focuses energy onto the detector. The detectors in the array either sense the heat of a body or detect low light levels.
While these systems have been used for military applications, the high cost of the scanning, cooling and optical systems associated therewith has heretofore limited the applicability of same for numerous other applications. Accordingly, there has been a need in the art for a low cost night vision system.
U. S. patent application Ser. No. 08/232,893 filed on Apr. 12, 1994 by S. H. Klapper et al. discloses and claims a low cost camera for night vision systems including a focal plane array of uncooled detectors and an optically fast, compact, optical arrangement for focusing energy from an input aperture onto the array. The array includes a plurality of pyroelectric detectors which, in the illustrative embodiment, are fabricated of barium-strontium-titanate material. Yet the characteristics and therefore the output of each detector is unique with respect to sensitivity, gain and DC (direct current) offsets by way of example. In addition, the DC offset of the detector is quite large and is typically much greater than its scene signal amplitude. Therefore, without any signal preprocessing, the detector DC offset will take up most of the dynamic range at the input of an analog-to-digital (A/D) converter. This leaves only a small portion of the A/D dynamic range for the useful detector scene signal. Thus, in order to really "see" the details of the scene signal, the A/D converter must have very high digitizing resolution. However, the higher the resolution of the A/D converter, the more expensive the A/D is, and the more bits are needed in the digital portion of the system. This results in a larger more expensive system.
The conventional technique for removing coarse DC offsets involves use of a capacitive element in series with the detector output. However, it would be prohibitively expensive to add a capacitor to each detector in an array of detectors which might include as many as 164.times.328 or 53,792 detectors.
Hence, while barium-strontium-titanate uncooled detector technology provides low cost infrared detection, conventional techniques for processing and displaying the output signals provided thereby are less than satisfactory for certain high performance, low cost applications. Thus, a need remains in the art for a system and technique for processing and displaying signals provided by uncooled barium-strontium-titanate infrared detectors.